Fitness-for-service (FFS) assessment is a
multi-disciplinary approach to determine whether equipment is fit for continued
operation. The equipment or system in question may contains flaws or other
damage, or may be subjected to more severe operating conditions than
anticipated by the original design. The outcome of a fitness-for-service
assessment is a decision to run as is, repair, re-rate, alter or retire the
equipment. A remaining life analysis may also be performed as part of the
assessment, which is used to set future inspection intervals and to budget for
capital expenditures when retiring existing equipment.

The three most common damage mechanism/flaw types
are as follows:

Metal
loss: including general thinning, local thinning, and pitting

Cracks
and planar flaws

Dents
and gouges

The advanced level of assessment is conducted
in accordance with best industry practice for fitness-for-service, and as
experts in the field, Quest Integrity was involved in developing these
guidelines. The codes that often used include: API 579/ASME FFS-1, BS7910, the
British Energy codes for high temperature assessments R5 and R6 and AS3788.

Metallurgical examinations and analyses,
including root cause and failure analysis

The figure below shows an assessment of a
storage tank that suffered significant dents during operation; a Level 3
fitness for service assessment was conducted to determine if a repair was required.
In this case, the tank passed the fitness-for-service assessment, which saved
the clients millions of dollars by avoiding unnecessary repair and downtime.

Advanced
Inspection

In addition to the advanced assessment services, Quest Integrity’s Australia
office also offers a wide variety of ultrasonic techniques including fully
automated and distance encoded:

Phased array methods (annular and linear)

Time of flight diffraction

Through transmission

Pitch and Catch

The inspection operators have experience with engineering and inspection
in a wide range of applications and industries requiring condition assessment.
Quest Integrity Australia’s inspection group is capable of conducting
inspection, analysis, and reporting on:

The inspection team also has significant experience in detecting damage
such as high temperature hydrogen attach (HTHA).

Recently Completed Projects
in the Refining and Syngas Industries

Remnant Life Assessment of Three Furnaces

Quest Integrity undertook Level 1 and Level 2 remnant
life assessments in accordance with API 530 and API 579 of three furnaces: a
vacuum charge heater, a delayed coker heater, and a hydrocracker heater. The
assets had been in service for approximately ten years and were approaching the
intended design life of 100,000 hours. They had also been subjected to
temperatures higher than the initial design temperature for four years.

First, a Level 1 assessment was performed based on
design data. The radiant section tubes from the furnaces did not pass the
assessment due to excessive creep damage.A Level 2 assessment was performed based on actual and operational data.
It was concluded that there was no immediate high risk of tube failure before
the next year plant turnaround, but that wall thinning due to corrosion would
have a large influence on remnant life of the tubes; therefore, it should be
inspected regularly. Each furnace was given new operating limits to complete
another 20,000 hours of service.

Engineering Critical Assessment of an Ammonia Storage
Tank

Quest Integrity conducted an assessment to determine
the safe use of a 1,400 ton capacity ammonia storage tank. As part of the assessment, Quest Integrity
recommended a future inspection strategy and frequency. The assessment involved
a review of the product characteristics, tank design, construction inspection
and quality control, operational history and hazard factors or hazard levels. Finite-element
(FE) stress analysis and a leak-before-break assessment (LBB) were also
implemented.

Engineering Critical Assessment of a Turbo Gas Expander

Quest Integrity performed an engineering critical
assessment of a gas expander rotor. The
gas expander operated for 15 months with the cooling air supply blocked causing
creep damage to the rotor’s blade location T-hooks. The main purpose of the
assessment was to determine whether the shaft would be fit-for-service under
continuous operation until the next scheduled outage. Finite element analysis (FEA) was used to
assess the stresses and determine the remnant life, taking into account
mechanical loading, thermal stresses and creep crack growth. Creep crack growth
calculations were performed using Signal™ Fitness-For-Service software from
Quest Integrity Group. The extent of accumulated creep damage was calculated
and found that the creep life fraction consumed totalled only 27%. It was
concluded that the gas expander was fit-for-service until shaft replacement in
2010.

Recently Completed Projects for the Hydro Power Industry

Fitness-for-Service
Assessment of a Turbine Headcover with Internal Erosion Damage

A turbine headcover suffered
from internal erosion-corrosion. Quest Integrity performed a Level 3
fitness-for-service assessment in accordance with API 579/ASME FFS-1 to
determine whether the wall loss was acceptable according to code requirements.
This involved Finite Element Stress Analysis. It was concluded that the headcover was acceptable for continued service.

Fatigue Assessment of a Pelton Wheel Shaft

Stress analysis, critical
flaw and fatigue assessments were performed on a pelton wheel turbine shaft.
Circumferential cracks which developed in the shaft near the runners had been
ground out during several shut downs. It
was a concern that the shafts were approaching the end of their serviceable
life, but the assessment provided the client with an inspection period for
future safe operation of their turbine.

Assessment of Spiral Casing

A fitness-for-service
assessment of a spiral casing was performed to evaluate if it was designed as
intended and determine if it was susceptible to failure caused by cracking in
the welds. A review of the material in
combination with the stress analysis showed that the spiral casing was fit-for-service.

For
more information, please contact Quest Integrity in Queensland, Australia: